To determine the mode of existence of structural lipids in the stratum corneum, lipids induced in the thick horny cell layers of guinea pig skin by n-hexadecane treatment were analyzed. Total lipids in the stratum corneum were extracted by Folch's solution and the ratio of phospholipids to free cholesterol was 1:8. Lipids extracted by non-ionic surfactant treatment appeared to originate from both the cell surface and intercellular space of the stratum corneum and the ratio of free cholesterol to phospholipids in this lipid fraction was much higher than that in the total lipids of the stratum corneum extracted by Folch's solution.